1. Field of the Invention
This invention relates to petroleum additive compositions, particularly to compositions which are in particulate form, water insoluble and characterized by slow, controlled oil-solubility at high temperatures and pourability at low temperatures. The invention especially relates to water insoluble, particulate compositions comprising petroleum additives, such as pour point depressants, paraffin inhibitors, corrosion inhibitors, biocides and the like, which compositions are slowly and controllably soluble in petroleum systems at elevated temperatures. The invention further relates to methods of inhibiting paraffin deposition, corrosion, rust, and bacterial and algal growth and a method of reducing the pour point of petroleum systems by virtue of incorporating therein the above-described compositions.
It is known that crude oils and heavier petroleum fractions, such as residual fuel oils, often contain substantial quantities of waxy materials. When such oils are subjected to temperatures below their cloud points, the waxy constituents tend to deposit on cool surfaces or crystallize and agglomerate into a solid gel. The gelling or stiffening of the oil introduces rheological problems which interfere with normal oil production and cause handling problems. High viscosities and high pour points result in additional production costs, such as increased horsepower, increased equipment size and increased fuel usage to heat the crude. Particularly affected by such rheological problems are long distance pipelines and offshore production facilities.
In addition to higher viscosities resulting from the gelling of petroleum, as described above, certain waxy fractions in crude oil may actually deposit directly on cold surfaces as the crude is exposed to cooler temperatures during production. The decrease in solubility of the waxy fraction with decreasing temperature results in wax deposits which reduce the volume of oil which can be produced. The addition of paraffin inhibitors helps to resolve wax deposition, but one of the greatest problems related to the use of paraffin inhibitors in most oilfield environments is the poor physical properties associated with these high molecular weight materials. Most effective treatment chemicals are either high melting solids or high pour point liquids or gells which pose a variety of handling problems in low temperature environments. The solids are handleable at ambient surface temperatures but dissolve too rapidly at high down-hole temperatures. The high molecular weight liquids frequently gel at ambient surface temperatures of 4.degree.-10.degree. C. or below and must be heated or diluted to be useful. Heated storage at the wellhead or dilution with solvents is normally required to allow continuous injection. Normal dilution may require as much as 95 to 98% solvent in order to achieve adequate application of paraffin inhibitor.
In view of the aforementioned problems, an object of the present invention is to provide compositions and methods for treatment of high temperature petroleum systems (i.e. down-hole) whereby the active ingredients of the composition do not immediately dissolve in the petroleum system but, instead, are gradually released over a period of time. At the same time, the compositions of the invention are particulate solids which are pourable at low ambient surface temperatures.
A further object is to provide paraffin inhibitor compositions and methods for treating high temperature petroleum systems.
Another object is to provide pour point depressant compositions and methods for treating high temperature petroleum systems.
2. Prior Art
Most of the chemical additives, e.g. pour point depressants and paraffin inhibitors, for crude oils make use of long alkyl side chains of from 14 to 30 carbon atoms spaced along a polymeric backbone. These branched chain structures cocrystallize with the paraffin waxes and reduce the size of the crystals and their tendency to form gelled structures and agglomerate on cold surfaces.
For example, French Pat. No. 82811 generally discloses a mixture of polyethylene with certain additives for the stabilization of gasoline.
British Pat. No. 1161188 discloses polymers containing aliphatic side chains of at least 14 carbon atoms formed by the polymerization of unsaturated compounds.
British Pat. No. 1274746 discloses the use of an ester of a copolymer of maleic anhydride and vinyl acetate where the ester is derived from an alcohol containing at least 20 carbon atoms.
U.S. Pat. No. 3,344,859 discloses the use of naphthalene as a paraffin inhibitor. The naphthalene is placed into the formation as a molten liquid but solidifies upon cooling to the formation temperature. The naphthalene then will slowly dissolve in the crude oil and allow a slow release of inhibiting agent.
U.S. Pat. No. 3,454,379 discloses the addition of polyethylene to improve the pumpability of distillate fuel oil.
U.S. Pat. No. 3,531,409 discloses solid solutions of polymers, e.g. polyethylene, with corrosion inhibitors and paraffin removers.
U.S. Pat. No. 3,630,280 discloses a method and composition for treating subterranean formations which consists of placing in the formation a solid mixture of high molecular weight ethylene/vinyl acetate, low molecular weight ethylene/vinyl acetate and a paraffin wax with a melting point between 135.degree. and 170.degree. F. This mixture allows slow controlled oil solubility in formations having temperatures between 125.degree. and 155.degree. F.
U.S. Pat. No. 3,640,824 discloses the use of a mixture of branched polyethylene with a molecular weight greater than 6000 and naphthalene and/or microcrystalline wax and/or asphaltenes as a paraffin inhibitor.
U.S. Pat. No. 3,661,541 discloses mixtures of (1) polymers of ethylene with polar monomers with (2) homopolymers or copolymers of ethylene to improve flow characteristics of distillate petroleum oils.
U.S. Pat. No. 3,879,177 discloses the use of a copolymer of maleic anhydride and vinyl methyl ether esterified with an alcohol containing 18 to 24 carbon atoms to inhibit the crystallization of wax and reduce its deposition on cold surfaces.
U.S. Pat. No. 3,926,579 discloses the use of alpha olefin polymers and copolymers as pour point reducers.
U.S. Pat. No. 4,175,926 discloses a flow improver for wax-containing petroleum light fuel which is a combination of an ethylene polymer and an ester copolymer or olefin polymer.
In addition to the above, numerous patents describe the addition of algaecides, rust inhibitors, corrosion inhibitors, biocides and the like into crude oil petroleum systems.